Pilot error probable cause of Ethiopian Airlines 737 crash

19 January, 2012

SOURCE: Flight International

BY: Dominic Perry

London

Ethiopian Airlines has angrily dismissed Lebanese investigators' conclusions over the fatal Boeing 737-800 crash off Beirut, sticking to its position that an unidentified problem, even sabotage, could have brought down the jet.

The carrier, backed by the Ethiopian civil aviation authority, has accused the inquiry of missing critical clues and lambasted it for not recovering much of the aircraft wreckage from the sea - a decision the inquiry believes was unnecessary given strong evidence that poor airmanship and disorientation resulted in a loss of control.

Ethiopian Airlines, which has defended its pilots throughout the two-year probe, has condemned the investigation as "biased, lacking evidence, incomplete and [failing to] present the full account of the accident". It insists eyewitness accounts of an explosion "clearly indicate" that the aircraft could have suffered a lightning strike or even been shot down.

"Recovery of the wreckage would have been crucial in determining whether fire was involved in the air," said the Ethiopian CAA. "Regrettably, the Lebanese side rejected the retrieval and the use of the wreckage in the investigation."

The Lebanese inquiry found that the January 2010 accident to flight ET409, only 4min 15s after departure from Beirut, was the result of the flightcrew's "mismanagement of the aircraft's speed, altitude, headings and attitude through inconsistent flight control inputs resulting in loss of control".

Night departure and course changes to avoid weather, combined with the captain's relative inexperience as pilot-in-command on the type, may have led to the captain "reaching a situation of loss of situational awareness similar to a subtle incapacitation and the [first officer's] failure to recognise it or to intervene accordingly", it added.

The inquiry found the aircraft had been out of trim from take-off, increasing the pilots' workload, and that only a "shy attempt" had been made to correct the situation. "Events were outpacing the crew," it said, and indicated that the pilots struggled to understand the aircraft's behaviour, and reacted incorrectly when the aircraft entered a stall.

During the short flight, the 737 followed an erratic course and flight recorders captured two "prolonged" stick-shaker alarms of 27s and 26s as the aircraft entered stall situations. There were also 11 aural "bank angle" warnings and a final overspeed warning towards the end of the 737's descent. Simulations indicated, however, that the aircraft remained recoverable until the final few seconds of flight as it passed 3,000ft at a high rate of descent.

The aircraft had a maximum angle of attack of 32°, maximum bank angle of 118° left, and maximum recorded speed of 407.5kt, said the report. No mechanical defects were found on the 2002 airframe (ET-ANB) and the two CFM International CFM56-7BE engines performed normally, it said.

It suggests that the pairing of the pilots may have been a contributory factor. The captain had logged only 188h in command of the 737-800, while the first officer had 673h, including 350h on type.

Although the pairing was within the airline's recommendations - it only restricts pairing captains with fewer than 300h and first officers with fewer than 100h - the report added: "That level of experience, although within the required approved standard, did not constitute a comfortable margin that would allow the crew to have enough confidence in the operation of the aircraft under demanding conditions, especially when we consider that the captain's experience on the 737-700/800 was acquired in the 51 days preceding the accident."

The first officer demonstrated a lack of assertiveness to intervene when faced with the captain's "strange flying behaviour", it added.

Ethiopian Airlines should revise its cockpit relationship management policies, it concluded, to stress the leadership and assertiveness required of a first officer, while crew pairings should also be reconsidered.